It is conventional technique to utilize B-stage compound to be a chip bond material, as disclosed in R.O.C. Taiwan Patent No. 455,970 entitled “multi-chip stacked package”. The conventional B-stage compound is used for adhering two chips, it won't produce a stress between the two chips because the two chips have a same thermal coefficient. Also the B-stage compound is sealed inside the molding compound, so that the adhesive strength of the B-stage compound is not demanded severely.
When a B-stage compound is directly configured to adhere a chip to a substrate in integrated circuit package. As showed in FIG. 1, at first a B-stage compound 13 is applied to the chip-attaching surface 11 of the substrate 10. Next, the back surface 23 of the chip 20 is compressed to the chip-attaching surface 11 of the substrate 10. The B-stage compound 13 is heated while compressed to become a fully cured C-stage film layer 13 that adheres the chip 20 to the substrate 10 during the chip-attaching step. The C-stage film layer 13 will not have any change in physical phase and any chemical reaction in the sequent process especially the molding step. Bonding wires 30 that are formed by wire-bonding technique connect the bonding pads 21 on the active surface 22 of the chip 20 with the pads 12 of the substrate 10, next a molding step is executed. However, the B-stage compound 13 is formed by printing or other liquid dispensing method so as not to have an attaching surface that is not flat completely, and cannot substantially adhere the chip 20 and the substrate 10 by the chip 20 attaching pressure. A popcorn defect is easy to happen while executing reliability test such as moisture or burn-in test after packaging. Therefore, when the chip 20 is separated from the substrate 10 prior to molding in a test, it is evident that the C-stage film layer 13 on the substrate 10 has a bad effective chip-bonding area merely 50% approximately against the entire chip-bonding region of the substrate 10, even smaller than 30% (as showed in FIG. 2). For that reason, the C-stage film layer 13 formed in chip-attaching step of the conventional process is not good enough to adhere the chip 20 and the substrate 10, also there are voids or gaps between the chip 20 and the substrate 10.